Spacer Length Alters CD37CAR-T Recognition See article p. 2862

T Cell Metabolism and COVID-19 See article p. 2900

Not So Exhausted CX3CR1+CD8+ T Cells See article p. 2924

ILF3 Negatively Regulates DC Maturation See article p. 2949

Protective Genotypes in Leukemia Relapse See article p. 3064

A Colorful View of Tonsils See article p. 3073

Chronic viral infections are associated with persistent Ag exposure, which can cause activated T cells to differentiate into dysfunctional exhausted T cells. Raju et al. (p. 2924) use single-cell RNA sequencing (scRNA-seq) to identify two subsets of exhausted CX3CR1+ CD8+ T cells that are generated in mice during chronic lymphocytic choriomeningitis virus (LCMV) infection. The CX3CR1+TIM3PD-1lo subset are quiescent and T-bet dependent and can be distinguished from the CX3CR1+TIM3+PD-1+ proliferative effector subset. The quiescent subset resembled TCF-1hi (CXCR5+ Ly-108/SLAMF6+) progenitor exhausted CD8+ T cells (TPEX). Further investigation of T-bet expression and pseudotime analysis indicated that TIM3CX3CR1+ cells may be precursors of TIM3+CX3CR1+ effector-like cells. During chronic LCMV infection, a large fraction of TCF+TOXlo memory-like CD8+ T cells appear to be derived from exhausted CX3CR1+CD8+ T cells. These results suggest that a subset of exhausted CX3CR1+CD8+ T cells have progenitor-like attributes that may contribute to the effector and memory-like CD8+ T cell pools during chronic infection.

In this Top Read, Liu et al. (p. 2900) examine how abnormal metabolic profiles in COVID-19 patients may alter T cell function. Ex vivo analysis of T cells from acutely infected COVID-19 patients showed higher levels of activation and apoptosis, as well as more severe defects in mitochondrial metabolism relative to T cells from convalescent patients or healthy controls. The authors also observed a direct correlation between IL-6 and C-reactive protein levels and mitochondrial mass in CD4 and CD8 T cells, and an indirect correlation with T cell fatty acid uptake. These data suggest a link between inflammatory conditions and metabolic dysfunction in resting T cells from acute COVID-19 patients. In vitro activation of T cells from acutely infected COVID-19 patients was associated with lower levels of glycolysis and reduced mTOR signaling. Together, these data indicate that acute COVID-19 disease may cause metabolic dysfunction in T cells and contribute to suboptimal adaptive immune responses.

The multiplex imaging method called ChipCytometry enables the analysis of tissue sections or cell suspensions using a technique in which cells are immunostained with fluorescently labeled Abs, are imaged, and then undergo photobleaching for another round of staining. These samples can be preserved and stored for several months after analysis and restained for different markers. In this Top Read, Hagel et al. (p. 3073) analyzed tissue sections from human palatine tonsils using ChipCytometry. The authors were able to visualize tonsillar architecture and could immunophenotype a range of CD3+ T cell subsets using supervised manual gating approaches or unsupervised clustering analysis. They also identified rare subsets, such as MAIT cells, in tissue sections and cell suspensions. Supervised and unsupervised approaches validated that tonsillar MAIT cells had a phenotype similar to MAIT cells found in peripheral blood. This study indicates that ChipCytometry may be a useful method for analyzing primary and secondary lymphoid organs prepared as tissue sections or as cell suspensions.

Previous studies have shown reduced leukemia relapse in patients receiving a haploidentical, T cell–depleted transplant from a donor with a killer cell Ig-like receptor (KIR) ligand different from the recipient. Donors with a KIR genotype that includes Cen B/B and/or multiple KIR B segments are associated with the greatest protection against relapse in recipients with C1-bearing HLA-C allotype. In this Top Read, Guethlein et al. (p. 3064) describe high-resolution KIR genotyping on a cohort of 890 donors to differentiate KIR alleles expressed as functional proteins from those not expressed. They identified two major forms of Cen B, termed Cen B01 and Cen B02. The latter appears to have evolved from Cen B01 and has deletions of several genes, including KIR2DL5. Cen B02 was also associated with better protection against relapse compared with Cen B01, which was related to donors having less inhibitory KIR. The authors also examined interactions between recipient HLA class I and KIR expressed on donor NK and T cells but did not detect any clinically meaningful trends. This study highlights the value of high-resolution KIR genotyping in understanding factors that protect against acute myelogenous leukemia relapse.

Myeloid dendritic cells (DCs) are critical for detecting pathogens via pattern recognition receptors (PRRs) to initiate innate immune responses. In this Top Read, Nazitto et al. (p. 2949) have identified IL enhancer binding factor 3 (ILF3) as a negative regulator of DC maturation and innate immune responses. Knockdown of ILF3 promoted monocyte-derived DC (MDDC) maturation and enhanced responses to innate immune ligands, but overexpression of a truncated (NF90) or long isoform (NF110) of ILF3 inhibited maturation and innate immune responses. The authors identified a nuclear localization sequence in ILF3 that was required for mediating these responses in MDDCs. ILF3-dependent genes were also shown to be enriched for genes linked to cholesterol homeostasis. Surprisingly, mutations in a zinc finger motif in NF110, but not NF90, inhibited the effects of ILF3 on DC maturation. These data define ILF3 as a transcriptional regulator in MDDCs that modulates DC maturation and curbs innate immune responses.

Chimeric Ag receptor T (CAR-T) cell–based therapies that target CD19 have revolutionized the treatment of B cell hematologic malignancies, including B cell acute lymphoblastic leukemia, but relapses continue to limit the long-term efficacy of this treatment. In this Top Read, Okuno et al. (p. 2862) evaluated CD37 as a potential B cell–specific target and engineered a CD37-targeting CAR-T cell. CD37 was expressed at high levels on human B cells in peripheral blood, as well as late-stage B cell precursors in the bone marrow, but expression was lower on early B cell precursors. The authors engineered a CD37CAR-T cell with a single chain variable fragment from a humanized anti-CD37 Ab, CD28 transmembrane and intracellular domains, and CD3ζ signaling domains. They optimized spacer lengths in the CD37CAR-T cell constructs for transfection efficiency and proliferation potential, and CD37CAR-T cells were able to target CD37-expressing human tumor cell lines with only limited effects on normal leukocytes. These findings indicate that CD37 may be another suitable target for CAR-T cell immunotherapy of B cell–based hematologic malignancies.